The explanations are important.

• I would hope that a modern employer would recognise work-life balance as a reasonable goal. Especially if you have a family or some similar responsibility.
• I would not say that you want to work on your own projects, which will make the employer suspect that you might goof off and work on them when you should be working for the employer, or that you might quit soon to work on them full time.
• You could say that you already have a part-time commitment and you need some more part-time work to build up your income. Make the part-time commitment sound commercial. For example "I need to do a little support some existing clients" is good, it gives an impression that you have some business sense. "I want to work on my own projects" is less good, it gives the impression that you might goof off to work on a pet open-source project.

The explanations are important.

• I would hope that a modern employer would recognise work-life balance as a reasonable goal. Especially if you have a family or some similar responsibility.
• I would not say that you want to work on your own projects, which will make the employer suspect that you might goof off and work on them when you should be working for the employer, or that you might quit soon to work on them full time.
• You could say that you already have a part-time commitment and you need some more part-time work to build up your income. Make the part-time commitment sound commercial. For example "I need to do a little support for some existing clients" is good, it gives an impression that you have some business sense. "I want to work on my own projects" is less good, it gives the impression that you might goof off to work on a pet open-source project.